Cisco 115 - OSPF Part 3

R5#show ospf interface g0/0
^ Displays info about OSPF on interface g0/0

R2(config)#int g0/0
R2(config-if)#ip ospf priority 255
^ Sets the priority of OSPF on an interface to "rig" future elections.  Recall that the DR/BDR election is 'non-preemptive'.

DR = Designated Router
BDR = Backup Designated Router

R5#clear ip ospf process
^ Don't do this in a production network.
Forces an election.  When the DR goes down, the current BDR will become the DR.  Then, an election will occur and this rigged router will become the BDR.  I guess the next election will cause this router to become the DR.

R5#show ip ospf neighbor
^ Displays info about OSPF neighbors and their state

 R3#show ip ospf interface brief
^ Displays interfaces and OSPF info for each

R3#show ip ospf interface g0/0
^ Displays detailed OSPF info on interface g0/0

Serial interfaces:
- DR and BDR are not elected because there are only 2 neighbors on the interface
- One side functions as DCE (Data Communications Equipment)
- The other side functions as DTE (Data Terminal Equipment)
- DCE needs to specify clock rate (speed) of connection

R1(config-if)#clock rate 64000
^ Sets the clock rate (bps) of the DCE router
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shut

Ethernet interfaces use the speed command.
Serial interfaces use the clock rate command.

Default encapsulation on serial interface is HDLC

R1(config)#int s2/0
R1(config-if)#encapsulation ppp
^ Sets encapsulation to PPP instead of the default HDLC
Encapsulation type must match on both ends.

R1#show controllers s2/0
^ This will reveal which side is the DCE vs the DTE

R1(config-if)#ip ospf network <type>
^ This command manually configures the OSPF network type with the following <type> options:
broadcast (Ethernet and FDDI)
non-broadcast (Frame Relay and X.25)
point-to-point (Serial)
point-to-multipoint

You might configure an Ethernet link between two routers since there is no need for a DR/BDR.  This might be a time to config a point-to-point network.

R2(config-router)#router-id 1.2.3.4
^ Configures the router-id of a router

The hello-interval and dead-interval values must match between OSPF neighbors:

R2(config-if)#ip ospf hello-interval <seconds>
^ Sets the number of seconds between hello announcements
Default is 10 seconds

R2(config-if)#ip ospf dead-interval <seconds>
^ Sets how long before the neighbor is considered dead
Default is 40 seconds

R2(config-if)#ip ospf authentication-key banana
^ Sets the authentication password to banana but does not yet enable authentication
R2(config-if)#ip ospf authentication
^ Enables authentication on the interface

R2(config-if)#ip mtu <number>
^ Sets the maximum size of an IP packet that can be sent ot of the interface. Defaults to 1500 bytes.
Must match on both neighbors or will have problems.

OSPF LSA types:
Type 1 - Router LSA - Identifies itself by stating its router ID and lists networks attached to the router's OSPF attached interfaces.
Type 2 - Network LSA - Generated by the DR of each 'multi-access' (broadcast) network. Lists the routers which are attached to the multi-access network.
Type 5 - AS-External LSA - Generated by ASBRs (Autonomous System Boundary Routers) to describe routes to destinations outside of the AS (Autonomous System) (OSPF domain)

R1#show ip ospf database
^ Displays LSDB (OSPF database) including neighbors, each router (type 1 LSA), network (type 2) LSA, and external link states (type 5)

 

 OSPF Neighbor process:

 

 

 

[These are my notes from Jeremy's excellent CCNA course which can be viewed here.]

 

 

Cisco 114 - OSPF Part 2

R3#show ip ospf interface f2/0
^ Displays OSPF info about interface f2/0. Includes cost info.

R3(config-router)#auto-cost reference-bandwidth <mbps>
^ Sets the reference bandwidth for better cost calculations.
The default reference bandwidth is 100 mbps which is the speed of Fast Ethernet.
On all your routers, set the reference-bandwidth to higher than your highest link.  This allows for later growth.

R1(config)#int g0/0
R1(config-if)#ip ospf cost 10000
^ Manually sets the ospf cost of an interface to 10000

Not recommended:
Another way to change the OSPF cost of an interface is with the bandwidth command.  Recall the formula to calculate OSPF cost is:
reference bandwidth / interface bandwidth

R1(config-if)#bandwidth <kbps>
^The interface speed does not actually change, but costs calculated with OSPF metrics use the bandwidth number.

R3#show ip ospf interface brief
^ Displays OSPF costs for each interface

R1#show ospf neighbor
^ Displays info about ospf neighbors

R1(config)#int g0/0
R1(config-if)#ip ospf 1 area 0
R1(config-if)#int g1/0
R1(config-if)#ip ospf 1 area 0
^ These commands specifically go into two interfaces and activates OSPF on them

R1(config-router)#passive-interface default
^ Configure ALL interfaces as OSPF passive interfaces

R1(config-router)#no passive-interface <int-id>
^ Turns off passive interface for specified interface

show ip protocols
^ Displays OSPF info




[These are my notes from Jeremy's excellent CCNA course which can be viewed here.]

Cisco 113 - OSPF Part 1

(config)#router ospf 1
^ Enters OSPF configuration mode.
The "1" is the process ID.
A router can run multiple OSPF processes at once.
Process ID is unrelated to area.

(config-router)#network 10.0.12.0 0.0.0.3 area 0
(config-router)#network 10.0.13.0 0.0.0.3 area 0
(config-router)#network 172.16.1.0 0.0.0.15 area 0
^ These three commands activate OSPF on all interfaces that match the given parameters.  They are configured as area 0.
The commands tell the router to find all interfaces that match the ranges specified.
Recall the network command uses wildcard matching.  So 0.0.0.15 = 255.255.255.240
Also recall that these commands don't specify which networks to advertise.
The commands activate OSPF on interfaces that fall in the range of the given wildcard matching patterns.

(config-router)#passive-interface g2/0
^ Tells the interface to stop sending OSPF 'hello' messages out that interface - probably because there are no further routers for that interface to neighbor with.
Use this command on any interface that doesn't have any OSPF neighbors.

(config)#ip route 0.0.0.0 0.0.0.0 203.0.113.2
^ Adds a default route and points to the next hop as the ISP's IP address
(This becomes our gateway of last resort)

(config-router)#default-information originate
^ This advertises the default route into OSPF so the other routers learn about it

R1#show ip protocols
^ Displays information about the routing protocol being used.
For us, that's OSPF

(config-router)#router-id 1.1.1.1
^ Manually configure the router ID as 1.1.1.1
The router will continue to use the old ID until we reload the router or use the command:
clear ip ospf process
^ Dangerous command because it clears out the routing map for a while until things are rebuilt.  This means downtime.

(config-router)#maximum-paths <#>
^ Change the maximum number of redundant paths that can be added to the routing table from 4 to #

(config-router)#distance <#>
^ Set the administrative distance

R4(config)#int l0
^ That's "L" 0 <-- Loopback0 (not the number 10)
This command creates a loopback interface
R4(config-if)#ip address 1.1.1.1 255.255.255.255
^ Assigns IP address 1.1.1.1/24 to interface Loopback0

R4>show ip int | begin Loop
^ Displays IP addresses assigned to interfaces beginning with the first match of "Loop" (Loopback0)

R4>show ip int brief
Shows a summary of interfaces and their IP assigned IP addresses

R4>show int l0
^ Again, that's loopback0, not the number 10
^ Command shows details of interface Loopback0

R1#show ip ospf neighbor
^ Shows OSPF neighbors

R1#show ip ospf database
^ Shows LSDB (link-state database)

R1#show ip ospf interface
^ Displays details about OSPF settings on each interface




[These are my notes from Jeremy's excellent CCNA course which can be viewed here.]